A mechanism was described for the cooperative generation of dislocation loops above a critical temperature in loaded solids. The massive dislocation activity which began near to the crack tip at the brittle-ductile transition temperature was modelled in terms of this mechanism and it was shown that it could explain the main features of the transition. In this model, the density of glissile dislocations remained essentially zero up to a certain temperature, and then increased sharply by several orders of magnitude within a temperature interval of less than 50K. This was similar to the sudden onset of dislocation activity that developed within a narrow temperature range around the brittle-ductile transition temperature. It was proposed that the cooperative generation of so many dislocations gave rise to the extensive plasticity at the transition temperature. The stresses in the crack-tip region were usually very high; of the order of 0.01μ. Thus, the crack tip environment was especially suitable for this mechanism to operate. The model was to be developed further in order to take account of the variation of the stress field in the vicinity of the crack under dynamic loading conditions.

Cooperative Generation of Dislocation Loops and the Brittle-to-Ductile Transition. M.Khantha, D.P.Pope, V.Vitek: Materials Science and Engineering A, 1997, 234-236, 629-32